Shiga toxin-producing Escherichia coli (STEC) O157:H7 is an important foodborne
disease worldwide, and cattle play a central role in the epidemiology of human E. coli
O157:H7 infection. Cattle feces are considered the primary source from which the food
supply and the environment become contaminated with this pathogen. Therefore,
reduction in the frequency and magnitude of fecal E. coli O157:H7 excretion by cattle is
predicted to decrease the incidence of human infection. Escherichia coli O157:H7 has
been sporadically isolated from other animals, and environmental sources. However, the
primary routes of dissemination of E. coli O157:H7 within and between farms remains
undetermined. The hypothesis that European starlings play a role in the dissemination of
E. coli O157:H7 between cattle farms was tested by determining if starlings inhabiting
Ohio dairy farms are a source for E. coli O157:H7 and other foodborne pathogens, and
evaluating the extent to which indistinguishable isolates of E. coli O157:H7 were shared
between dairy farms located in a close geographic proximity. Cultured intestinal contents
of starlings captured on Ohio dairy farms showed that starlings seasonally harbor E. coli
O157:H7 (late summer 20%, winter 0%) and other STEC (62.5%).
ii
Stx-negative O157 isolates could be lysogenized by stx2-converting bacteriophage,
indicating that these toxin-negative strains may acquire stx2.
Pulsed-field gel electrophoresis analysis of E. coli O157:H7 isolates recovered during
a longitudinal study of 20 dairy farms in Ohio showed E. coli O157:H7 subtypes (four
indistinguishable subtypes) were disseminated with considerable frequency among farms
(7 of 20) in close geographic proximity and non-bovine sources may have contributed to
the transmission of this organism between farms.
In summary, these data support a role of wild birds in the dissemination of E. coli
O157:H7 among dairy farms, but the extent of their role in dissemination of this pathogen
is yet to be determined.
iii